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Year : 2020  |  Volume : 43  |  Issue : 1  |  Page : 26-30  

Assessment of radioactivity of different types of houses in Imphal city, Manipur, India

1 Department of Zoology, D. M. College of Science, Imphal, Manipur, India
2 Department of Physics, Oriental College (Autonomous), Imphal, Manipur, India
3 Department of Radiation Oncology, Regional Institute of Medical Sciences, Imphal, Manipur, India

Date of Submission28-Dec-2019
Date of Decision20-Jan-2020
Date of Acceptance18-Mar-2020
Date of Web Publication12-May-2020

Correspondence Address:
B Arunkumar Sharma
Department of Radiation Oncology, Regional Institute of Medical Sciences, Imphal, Manipur
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/rpe.RPE_42_19

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An assessment of radioactivity concentration of different types of houses was conducted at 437 houses of Imphal City, Manipur, India. The average annual effective doses of gamma radiation level in indoor and outdoor were determined as 1.22 ± 0.09 (range: 0.79–1.41) mSvy-1 and 0.79 ± 0.08 (range: 0.57–1.07) mSvy-1 for reinforced cement concrete houses, followed by 1.06 ± 0.08 (range: 0.84–1.27) mSvy-1 and 0.78 ± 0.08 (range: 0.59–0.94) mSvy-1 for Assam-typed (AT) brick houses, 0.85 ± 0.08 (range: 0.63–1.28) mSvy-1 and 0.76 ± 0.08 (range: 0.52-1.01) mSvy-1 for AT mud houses, 0.77 ± 0.08 (range: 0.58–0.96) mSvy-1 and 0.73 ± 0.07 (range: 0.65–0.85) mSvy-1 for AT katcha houses, and 1.04 ± 0.07 (range: 0.88–1.22) mSvy-1 and 0.73 ± 0.07 (range: 0.65–0.84) mSvy-1 for adobe laid earthen houses, respectively. Moreover, the annual effective dose conceived from building materials was recorded as 1.8 mSvy-1 from sand, 1.5 mSvy-1 from brick, and 1.0 mSvy-1 from Portland cement. The worldwide average indoor dose limit of radon conceiving and its decay product by inhalation is 1.15 mSvy-1 prescribed by the UNSCEAR (2000).

Keywords: Different house types, effective dose, Imphal, Meitei Yumjao, radioactivity

How to cite this article:
Suranjit S, Singh OS, Singh S N, Sharma B A. Assessment of radioactivity of different types of houses in Imphal city, Manipur, India. Radiat Prot Environ 2020;43:26-30

How to cite this URL:
Suranjit S, Singh OS, Singh S N, Sharma B A. Assessment of radioactivity of different types of houses in Imphal city, Manipur, India. Radiat Prot Environ [serial online] 2020 [cited 2023 May 30];43:26-30. Available from: https://www.rpe.org.in/text.asp?2020/43/1/26/284231

  Introduction Top

Terrestrial background radiations

The level of terrestrial radiation differs from place to place around the world, as the concentration of materials in the earth's crust varies[1] and depends on their emanation rate from the soil, meteorological, geological, and geographical factors and height above the ground surface.[2] The main radionuclides in building materials are from the238 U and232 Th decay chains and40 K.

Radon is an inert, naturally occurring radioactive gas,[3] which is considered the second leading cause of lung cancer;[4],[5] besides, it can be more concentrated in indoor than outdoor. The exposure to radon is due to the emanation by decaying terrestrial radionuclide238 U and232 Th. The gamma radiation arising from the walls, floors, and ceilings is the major source of gamma radiation exposure[6] due to the materials used for building construction containing elevated levels of radioactivity.[7] Most of the people spending their maximum time (approximately 80%) of a day in indoor.[8],[9] The average indoor effective dose due to gamma rays from building materials is estimated to be about 0.4 mSvy-1.[10] A study on building materials showed that granite and phosphogypsum are the highly radioactive materials which enhance indoor absorbed dose rate up to five times than the dose criterion.[11] Another study showed that building materials collected from Yan'an, China, may be used safely as construction materials.[12] This suggests that the effective radiation dose rate in indoor depends on the level of radioactivity in the soil, rock, and industrial by-products from where these building materials are derived. Hence, the knowledge of the level of natural radioactivity in building materials is, thus, become important to assess any possible radiological risk to human health and develop any precautionary measures in using building materials.

The present study area, Imphal City, is the capital of Manipur and it includes two valley districts, namely, Imphal-East and Imphal-West. Radioactive contaminants as well as indoor and outdoor radiation dose rates for five different types of houses available in this area were studied. As per census of 2011, Imphal-West district is the most populous district, which has a population density of 930 inhabitants per square kilometer (km ) with a total population of 517,992 and covers a total area of 558 km . It is located at 24°49'N, 93°54'E,[13] whereas Imphal-East district is the second most populous district having a population density of 638 inhabitants per square kilometer with a total population of 452,661 and covers a total area of 710 km . It is located at 24°48'N, 93°57'E.[14] Besides, Imphal City is about 300 km away from Domiasiat in Meghalaya which is known for huge deposited area of heavy minerals in the country.[15]

  Materials and Methods Top

In-house survey by survey meter

Indoor and outdoor background gamma radiations of different types of houses were measured using a NaI (Tl) scintillator-based microroentgen survey meter (SM) manufactured by Nucleonix Systems Pvt. Ltd., Hyderabad, India, having a sensitivity of 1 μ Rh-1. It was used for instantaneous measurement of dose rate by keeping the SM at a height of about 1 m above the ground surface. Repeated measurements not <10 times for each spot were taken. The average value for all these ten measurements was assumed to be the dose rate for that particular area.[9] Total measurements of 437 different houses were covered during the study.

Radiological analysis of building materials

A total of 9 samples of building materials from Imphal City were collected and crushed into small sizes. The samples were subjected to dry in a hot air oven at 110°C for 24 h. The Portland cement samples were also dried at 60°C. Then, ground into fine powder, homogenized, and sieved through a mesh size of 0.45mm;[16] sealed and stored it carefully for a period of 4 weeks at room temperature to reach secular equilibrium.[7],[15]

A 3 ”X3 ” NaI (Tl) scintillation detector based Gamma spectrometer was employed with adequate shielding (about 10 cm lead). The efficiency calibration of the gamma ray spectrometer was made using different energy peaks covering the range up to ≈ 2000 keV. Measurements were performed using calibrated standard source samples, which contain a known activity of gamma ray emitters radionuclides namely133 Ba (356.1 keV),137 Cs (661.6 keV),60 Co (1173 KeV and 1332 KeV) and226 Ra (1764.5 keV). The activity concentrations of226 Ra,232 Th, and40 K in the sample of 300 g were determined with adequate shielding. The counting time was preset at 36,000 s.[18] The activities concentration of226 Ra was determined from the average activity concentration obtained from the prominent gamma lines of214 Bi and214 Pb and that of232 Th was obtained from the average concentration obtained from the gamma lines of212 Bi,228 Ac,208 Tl, respectively. however,40 K was evaluated from its own gamma photopeak.[15],[16],[19]

The activity concentrations of238 U,232 Th series, and40 K were calculated using the following equation;[20]

A (Bqkg-1) = N/εβM(1)

Where N = the net gamma counting rate (counts per se cond), ε = the detector efficiency of the specific gamma-ray, β = the absolute transition probability of gamma decay, and M = the mass of the sample (kg).

The relative concentration and distribution of226 Ra,232 Th, and40 K did not uniform in environment and not found to be uniform in building materials. Radium equivalent (Raeq) activity index is introduced to represent the specific activity of226 Ra,232 Th and40 K by a single quantity.[7],[21],[22] The index parameter Raeq is related to exposure to radiation and defined to compare the specific activity of material containing different activities of238 U,232 Th, and40 K.[23] Thus, radium equivalent activity (Raeq) is computed using the equation:[10],[24]

Raeq= ARa+ 1.4ATh+ 0.077AK (2)

Where ARa, ATh, and AK are the specific activities of226 Ra,232 Th, and40 K in Bqkg−1, respectively.

Activity concentration index, or gamma index I, is defined in order to examine the applicability of using building materials in construction. It is defined by the following expression:[25]

I = ARa/300 + ATh/200 + AK/300 ≤ 1 (3)

This is a simple criterion of the applicability of a building material.

Adsorbed dose rate (D): The absorbed Dose Rate due to gamma radiation in air for a standard room dimensions and for common building materials with naturally occurring radionuclides226 Ra,232 Th and40 K was calculated using the guidelines given in UNSCEAR (2000):[10]

D (nGyh-1) = (0.92 × ARa) + (1.1 × ATh) + (0.08 × AK) (4)

The annual effective dose (Deff) was calculated by applying the dose conversion factor of 0.7 SvGy-1 from the absorbed dose in air received by an adult and a value of 0.8 as an indoor occupancy factor (assuming 80% of an individual time is spending in indoor).[10],[22],[26] The annual effective dose (Deff) due to gamma radiation from building materials was evaluated as:

Deff(mSv/y) = D(nGyh-1) × 8760 h × 0.8 × 0.7SvGy-1 × 10-6 (5)

  Results and Discussion Top

Background gamma dose rate and corresponding annual effective dose rate of different types of houses were estimated at 437 houses in Imphal City, Manipur, NE, India. During the survey, approximately five different types of houses were classified, which is based on their building materials utilized which are derived from soils and rocks in and around Imphal City. The classified houses are shown in [Figure 1].
Figure 1: Illustration of different types of houses which is available in the Imphal, Manipur, India. (a) Typical picture of reinforced cement concrete house. (b) Typical picture of Assam-typed brick house. Typical picture of Assam-typed mud house. (d) Typical picture of Assam-typed katcha house. (e) Typical picture of adobe laid earthen house (an indigenous-traditional house of Manipur) so called as Meitei Yemjao in Imphal

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In the survey, the average annual effective dose rates of gamma radiation level in indoor and outdoor were determined [Table 1] as 1.22 ± 0.09 mSvy-1 and 0.79 ± 0.08 mSvy-1 for RCC houses, followed by 1.06 ± 0.08 mSvy-1 and 0.78 ± 0.08 mSvy-1 for AT brick houses, 0.85 ± 0.08 mSvy-1 and 0.76 ± 0.08 mSvy-1 for AT mud houses, 0.77 ± 0.08 mSvy-1 and 0.73 ± 0.07 mSvy-1 for AT katcha houses, and 1.04 ± 0.07 mSvy-1 and 0.73 ± 0.07 mSvy-1 for adobe laid earthen house, respectively.
Table 1: Annual effective dose of different types of houses in Imphal City

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Meanwhile, the annual effective dose from building materials was recorded as 1.76 mSvy-1 from sand, followed by 1.53 mSvy-1 from brick and 1.04 mSvy-1 from Portland cement [Table 2]. The average gamma index of bricks and sand was observed higher than unity.
Table 2: Radiological parameters of building materials used in Imphal City

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Average annual effective dose of 1.22 ± 0.09 mSvy-1 of RCC houses was slightly higher than the maximum permissible dose limit for nonradionuclide industrial workers and the public as 1 mSvy-1 recommended by International Commission on Radiological Protection.[27] The average effective dose rate from RCC houses as evaluated from its building materials, namely, sand, cement, and bricks, was also obtained as 1.44 ± 0.36 mSvy-1.

The adobe laid earthen typed houses are gradually decreased in its number because of the modernization of building materials and urbanization. The indoor average effective dose rate of such type of houses as evaluated by SM was 1.04 ± 0.07 mSvy-1. However, the annual effective dose rate evaluated from soil of Imphal City as reported earlier[15] was 1.1 mSvy-1.

The Assam-type brick houses are less in number compared with RCC houses. The indoor average effective dose rate of such type of houses as evaluated by SM was 1.06 ± 0.08 mSvy-1. The effective dose rates of the remaining Assam-type mud houses and Assam-type katcha houses were observed as 0.85 ± 0.08 mSvy-1 and 0.77 ± 0.08 mSvy-1, respectively.

The outdoor effective dose rate of the Imphal City was observed in the range of 0.52–1.07 mSvy-1, which is in agreement with the earlier study of Sharma et al.[15]

  Conclusions Top

The average radioactive contaminant of building materials available in different types of houses of Imphal City were found: for bricks,226 Ra – 32.86 Bqkg−1, 232 Th – 140.19 Bqkg−1, and40 K – 1596.41 Bqkg−1; for sand,226 Ra – 46.62 Bqkg−1, 232 Th – 129.36 Bqkg−1, and40 K – 2159.62 Bqkg−1; and for cement,226 Ra – 34.96 Bqkg−1, 232 Th – 34.12 Bqkg-1, and40 K – 1766.53 Bqkg-1. Indoor effective dose rate of RCC houses is observed higher than other remaining types of houses. Assam-type katcha houses and mud houses show minimal effective dose rates.


The present study is the outcome of investigations carried out by the authors. The authors express their gratefulness to the Institutional Biotech Hub Laboratory, D. M. College of Science, Imphal, Manipur, under Department of Biotechnology, Ministry of Science and Technology, Government of India, New Delhi, and Environment Radiation Dosimetry Laboratory, Oriental College (Autonomous), under Atomic Energy Regulatory Board (AERB), Bombay, Government of India, New Delhi, for providing the laboratory support necessary for this study.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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  [Figure 1]

  [Table 1], [Table 2]


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